Deenameling process



Patented Jan. 29, 1952 DEENAMELING PROCESS Arthur M. Lander, Park Ridge, 111., assignor to.

Lawndale Enameling 00., Chicago, Ill., a corporation of Illinois No Drawing.

10 Claims.

This invention relates to a de-enameling process. The invention is particularly useful in the de-enameling of porcelain enamel on steel parts so that the steel parts are placed in good condition for re-enameling.

. The de-enameling of enameled pieces has long presented a problem, and because of the loss of metal, difficulty of treatment, cost, and other factors, the question has been debated as to whether de-enameling is desirable. In prior de-enamelmg processes acid, molten caustic and boiling caustic have been used in separate processes for the removal of the enamel, and sandblasting has also been employed. Each of the processes has severe limitations, and defects in the product often result. In the use of sandblasting a very substantial amount of the metal is lost (sometimes up to 50%), and the piece often buckles or becomes distorted or warped during the blasting operation, which is usually conducted at a pressure of from 80 to 90 pounds. In the treating processes using acid, caustic, etc., long periods of time are required which often render these processes impracticable. I

An object ofthe present invention is to provide a de-enameling process which may be carried through in a minimum of time while, without substantial loss of metal, at the same time preparing the metal eflectively for re-enameling. A further object is to provide a two-step process in which the piece is de-enameled without substantial loss of metal, without injury to the piece, and while at the same time providing a surface on the piece particularly suited for receiving a new enamel coating. Yet another object is to provide a process in which the piece is treated in such a manner so that it may be sand-sprayed at relatively low pressures to provide a wellfinished piece suitable for re-enameling, while at the same time substantially eliminating metal loss. Other specific objects and advantages will appear as the specification proceeds.

In one embodiment of my invention the enameled piece to be treated is immersed in a tank containing sodium hydroxide and sodium silica fluoride solution heated to about 280 to 350 F. If desired, a wetting agent may be added to the solution. The water content of the solution is maintained by spraying water over the top surface, and heat is maintained by the use of gas immersion burners or other suitable means. The a piece to, be treated is allowed to stay in the tank from two to four hours, depending upon the thickness of the enamel to be removed. The piece is then removed fromthe tank and rinsed, preferably with boiling water, and thendried. The

Application January 25, 1950, Serial No. 140,565

piece is then sand-sprayed at from 30 to 40 pounds air pressure, and after this treatment is ready for re-enameling.

In the foregoing process I prefer to employ a solution containing from 8 to 12 pounds of sodium hydroxide and from /2 to 1 pound of sodium silica fluoride per gallon of water. If a wetting agent is used I prefer to use from /2 to 3 pounds of the wetting agent.

The preferred operating temperatures are 290 to 310 F., but these may be varied depending upon the thickness of the enamel of the piece being treated. During the heating step it is important that make-up water be returned to the tank, and I prefer to do this by spraying the water upon the top of the solution.

In the sand-spraying operation I prefer to use a pressure of from 30 to 40 pounds, but it will be found desirable on some pieces to raise the pressure to about pounds. The spraying of the abrasive at such low pressures is found to remove the black residue left on the metal after the above treating operation, while at the same time leaving the surface of the metal in a slightly roughened condition adapting it for re-enameling. The

black sludge film or residue on the piece provides a marker enabling the operator to sand-spray the surface evenly while at the same time such residue seems to co-operate with the abrasive in leaving an evenly roughened surface excellently adapted for the re-enameling step.

By the above process it is found that the pretreating step with caustic, etc, enables the final application of sand-spraying to be accomplished at low pressures, so that at no time is the metal subjected to heat which would tend to buckle or distort the metal. As a result the piece is deenameled without loss of metal, while at the same time the surface is roughened for the new enameling step; thus there is no greater loss of metal than when new pieces (which have never before been enameled) are being roughened for the enameling operation. 7

Specific examples of the process may be set out as follows: I

Example 1 A steel panel having porcelain enamel thereon was immersed in a tank containing iipounds of sodium hydroxide. pound of sodium silica fluoride, and pound of wetting agent (Quaker vitro-stripi. The temperature was maintained at about 290 F., and replacement water was added constantly by spraying the same upon the top surface of the solution. After about two hours the panel was removed and rinsed with Example 2 A steel panel surfaced with porcelain enamel was immersed in a tank containing 12 pounds of sodium hydroxide, 1 pound of sodium silica fluoride, and 3 pounds of wetting agent (Quaker vitrostrip) per gallon of water. The solution was maintained at a temperature of around 350 F., replacement water being added by spraying the same on to the top surface of the solution. The panel was allowed to stay in the tank about three hours, and upon removal was rinsed in a boiling water solution. The panel was then dried and the dried panel sand-sprayed at about 40 pounds air pressure to remove the black residue thereo and-.to roughen the surface. I

Example '3 piece. The piece was then dipped in a tank containing from 5' to H2804 solution maintained' at a temperature of about 170 F. The

piece was thereafter again dipped in a rinse tank of boiling water and then immersed in a neutralizing tank containing a solution of .5-2% sodium hydroxide, preferably maintained at a temperature of about 180 F. The piece was then passed from the neutralizing tank through a dryer, which was maintained at a temperature of 250-350" F., and when dried passed through a sand-spray apparatus where it was subjected to sand delivered under air pressure of about 40 pounds per square inch.

In all of the foregoing examples it will be noted that a minimum of time is required. Instead of treating the panel in solutions for 10 to 24 hours or so as in the prior boiling caustic method, the panel is treated for approximately two hours and then subjected, after drying, to sand-spraying at low pressures, the latter operation requiring just a few minutes.

While in the foregoing specification I have set forth specific steps in considerable detail for the purpose of illustrating embodiments of the invention, it will be understood that such details may be varied widely by those skilled in the art without departing from the spirit of my invention.

I claim:

1. In a de-enameling process, the steps of immersing the enameled piece in a bath of sodium hydroxide and sodium silica fluoride solution at a temperature of from about 280 to 350 F. dissolve the enamel while leaving a film of sludge on the surface of the piece, and sand-spraying the piece at pressures of from 30 to 60 pounds to remove the sludge film therefrom.

2. In a de-enameling process, the steps of im mersing the enameled piece in a bath of sodium hydroxide and sodium silica fluoride solution at a temperature of from 280 to'350" F. to dissolve the enamel while leaving a film of sludge on the surface of the piece, rinsing the piece with boiling water and sand-spraying the piece at pressures of from 40 to 60 pounds to remove the sludge film therefrom. r

3. In a de-enameling process, the steps of immersing the enameledpiece in a bath of sodium hydroxide and sodium silica fluoride solution at a temperature of from 280 to 350 F. to dissolve the enamel while leaving a film of sludge on the surface of the piece, rinsing the piece with boiling water, drying, and sand-spraying the piece at pressures of from 40 to 60 pounds to remove the sludge of film therefrom.

4. In a de-enameling process, the steps of immersing the enameled piece in a bath of sodium hydroxide and sodium silica fluoride solution in the presence of a wetting agent and at a temhydroxide and sodium silica fluoride solution in I the presence of a wetting agent and at a temperature of from 290 to 310 F. for a period of from two to four hours to dissolve the enamel while leaving a film ofsludge on the surface of the piece, and sand-spraying the piece at pressures of from 30 to 60 pounds to remove the sludge film therefrom.

6. In a de-enameling process, the steps of immersing the enameled piece in a bath of sodium hydroxide and sodium silica fluoride solution in the presence of a wetting agent and at a temperature of from 290 to 310 F. for a period of from two to four hours to dissolve the enamel while leaving a film of sludge on the surface of the piece, and sand-spraying the piece at pressures of from 30 to 40 pounds to remove the sludge film therefrom.

7. In a de-enameling process, the steps of immersing the enameled piece in a bath of sodium hydroxide and sodium silica fluoride solution at a temperature of about 290-to 310 F. and for a period of from two to four hours to dissolve the silica of the enamel while leaving a film of sludge on the surface of the piece, and then sandspraying the piece at a pressure of from 30 to 60 pounds to remove the sludge film therefrom.

8. In a de-enameling process, the steps of immersing the enameled piece in a bath of sodium hydroxide and sodium silica fluoride solution in which the sodium hydroxide is from 8 to 12- pounds and the sodium silica fluoride from to 1 pound per gallon of water, maintaining the bath at from about 280 to 350 F. to dissolve the enamel, and while leaving a film of sludge on' the surface of the piece, and then sand-spraying the piece at pressures of from 30 to 60 pounds to remove the sludge film therefrom.

9. In a de-enameling process, the steps of immersing the enameled piece in a solution bath containing from am 12 pounds of sodium hydroxide, from to 1 pound of sodium silica fluoride, and from to 3 pounds of wetting agent per gallon of water, maintaining the solution at a temperature of from about 280 to 350 F., removing the enameled piece from the solution after from twoto four hours, during which time the enamel isdissolved and a film of sludge formed on the surface of the piece, rinsing the piece with boilin; water, drying the piece and sand-spraying the piece at pressures of from 30 to 60 pounds to remove the sludge film therefrom.

10. In a de-enameling process, the steps of immersing the enameled piece in a solution bath containing from 8 to 12 pounds of sodium hydroxide, from to 1 pound of sodium silica fluoride, and from to 3 pounds of wetting agent per gallon of water, maintaining the solution at a temperature of from about 290 to 310 F., removing the enameled piece from the solution after from two to four hours, during which time the enamel is dissolved and a film of sludge formed on the surface of the piece, rinsing the piece with boiling water, drying the piece and sand-spraying the piece at pressures of from 30 to 40 pounds to remove the sludge film therefrom.

ARTHUR L. LANDER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 10 Number Name Date 1,829,693 Ward Oct. 2'7, 1931 1,923,828 Janota Aug. 22, 1933 2,158,063 Broadfield May 16, 1939 2,488,068 Roman Nov. 15, 1949 

1. IN A DE-ENAMELING PROCESS, THE STEPS OF IMMERSING THE ENAMELED PIECE IN A BATH OF SODIUM HYDROXIDE AND SODIUM FLUORIDE SOLUTION AT A TEMPERATURE OF FROM ABOUT 280 TO 350* F. DISSOLVE THE ENAMEL WHILE LEAVING A FILM OF SLUDGE ON THE SURFACE OF THE PIECE, AND SAND-SPRAYING THE PIECE AT PRESSURE OF FROM 30 TO 60 POUNDS TO REMOVE THE SLUDGE FILM THEREFROM. 